System for checking the pressure of the tires of a vehicle

ABSTRACT

The system for checking the pressure of the tires of the wheels ( 2-5 ) of a vehicle includes individual wheel-checking devices, each with a pressure sensor and a transmitter ( 20, 30, 40, 50 ), a central unit ( 1 ) with a common receiver ( 12 ) and antenna means ( 21-25 ), comprising individual receiving antennae ( 22-25 ) associated respectively with the wheel locations ( 2-5 ), working with the transmitters ( 20, 30, 40, 50 ), and the antenna circuits of the central unit ( 1 ) additionally comprise a main antenna ( 21 ) for monitoring all the pressure-checking devices ( 20, 30, 40, 50 ) and circuits ( 13 ) for switching over the common receiver ( 12 ) from the main monitoring antenna ( 21 ) onto each of the individual acquisition antennae ( 22-25 ).

A system for checking the pressure of the tires of a motor vehicleincludes, around a central computer equipped with a receiver, with itsreceiving antenna, individual checking devices, one per wheel, eachcomprising, inserted into the rim, a pressure sensor and a transmitter,with its transmitting antenna. Each device has to transmit regularly, tothe central computer, bursts of information bits relating to thepressure of the associated tire, and it has to transmit a defined numberof them, generally five, all identical, so that another defined number,generally two, of these bursts should be received and so that it cantherefore be considered that the information at that instant hasactually been transmitted and received. The transmission of the burstscan take place, to give an idea, every hour, if the vehicle is at rest,every six minutes, if the vehicle is running.

The system developed above exhibits the drawback that, after havingchanged the wheels, the system may detect a lack of pressure at onewheel which is not actually a faulty wheel. With the bursts ofinformation bits being in effect “signed” by their respective wheels,if, for example, the two front wheels are changed over and then thepressure of the left wheel falls, the system will indicate that it isthe original right wheel, which has become the left wheel, which isfaulty.

DE 195 18 806 teaches a radio system for checking the pressure of thetires, with antennae associated electromagnetically with the locationsof the respective wheels, in order to identify them.

However, as the transmitter devices of the wheels are mutuallyindependent, their transmissions are asynchronous and the centralreceiver has to be able to detect every start-of-transmission so as tosynchronize itself and to receive the information transmitted.

The present application claims to have a solution to this problem.

The invention thus relates to a system for checking the pressure of thetires of the wheels of a vehicle including individual wheel-checkingdevices, each with a pressure sensor and a transmitter, a central unitwith a common receiver and antenna means, comprising individualreceiving antennae associated respectively with the wheel locations,configured to work with the transmitters of the individual checkingdevices, the system being characterized in that the receiving-antennameans of the central unit additionally comprise a main antenna formonitoring all the pressure-checking devices and means for switchingover the common receiver of the central unit from the main monitoringantenna onto each of the individual acquisition antennae.

Thus, with the main monitoring antenna having made it possible to detectthe failure of a tire, as yet undefined, one of the individual antennaewill make it possible to acquire the identification of the tireconcerned. Any difficulty relating to the asynchronous transmission fromthe wheel devices is thus avoided.

Advantageously, with the wheel-checking devices being configured toperiodically transmit bursts of information bits, thechangeover-switching means are configured to switch over from the mainreceiving antenna onto an individual receiving antenna in the course ofthe same burst period.

If, after switching over, the common receiver receives the rest of thebursts, then it is the wheel tire associated with the individual antennaconcerned which is actually the faulty tire. Otherwise, the followingburst period will be awaited in order to switch over to anotherindividual antenna and so on until the faulty wheel tire has beenidentified.

Very advantageously, the receiving antennae are radiating cables.

The invention will be better understood with the aid of the followingdescription of a preferred embodiment of the tire-pressure checkingsystem, by reference to the attached drawing, in which:

FIG. 1 is a functional block diagram of the pressure-checking device,and

FIG. 2, formed by FIGS. 2A, 2B, 2C, 2D, 2E and 2F, is a timing diagramillustrating the operation of it.

The tire-pressure checking device of FIG. 1 is mounted on a motorvehicle, of which only the four wheels 2, 3, 4 and 5 are representeddiagrammatically. It includes a central unit 1 linked at its input byradio to the wheels 2 to 5.

The wheels 2 to 5 each include an individual wheel-pressure checkingdevice, referenced 20, 30, 40 and 50 respectively, each including aradio transmitter, 29, 39, 49, 59 respectively, powered by battery,associated with a pressure sensor, 28, 38, 48, 58 respectively, in orderto transmit pressure telemetry to the central unit 1. The latter, tothat end, includes a plurality of receiving antennae, four individualantennae 22, 23, 24 and 25 to be precise, and a main monitoring antenna21.

The central unit 1 includes a timebase 10 linked to a microprocessor 11which is itself linked to the output of radio-receiver circuits 12 towhich the antennae 21 to 25 are connected. The microprocessor 11controls antenna-switching circuits 13 belonging to the radio circuits12.

The radio-receiver circuits 12 form a common receiver for all theantennae 21 to 25, which work with the respective transmitters 29, 39,49, 59 of the individual devices 20, 30, 40, 50 for checking the wheels2 to 5 and the antennae 22 to 25 of the central unit 1 are individualreceiving antennae associated respectively with the wheel locations ofthe vehicle. Each individual antenna 22 to 25 thus includes at least onesegment, an end segment in the figure, situated in immediate proximityto the associated wheel 2 to 5 so as to form a one-to-oneelectromagnetic association between the transmitter of the wheel 2 to 5in question and the segment of the associated antenna 22 to 25. In otherwords, the individual receiving antennae 22 to 25 areelectromagnetically associated, in a one-to-one way, with the respectivewheel locations 2 to 5 and thus each constitute an antenna for selectiveacquisition of the telemetry from the associated pressure-checkingdevice 20, 30, 40, 50.

Apart from the receiving segment above, each individual antenna, such as22, can be screened so that it remains insensitive to the radiation fromthe other three transmitters 39, 49, 59 of the wheels 3 to 5 which arenot associated with the antenna 22.

In this example, the individual, short-range antennae 22 to 25 areradiating cables forming a proximity sensor.

Thus, each individual antenna 22 to 25 transmits, to the radio-receivercircuits 12, only the transmissions from the checking device 20, 30, 40,50 of the associated wheel 2 to 5. The central unit 1 identifies theindividual antenna 22 to 25 then switched in, or polled, at the input tothe radio circuits 12 by the circuits 13 according to the routing orselection addresses or orders which have been transmitted to the latterby the microprocessor 11, a correspondence table in memory indicatingthe individual antenna 22 to 25 concerned on the basis of the routingaddress. The central unit 1 can thus associate with the radio datareceived by the circuits 12 a defined wheel location 2 to 5 and thus, inthe event of a lack of pressure, signal the position, or the location,of the wheel 2 to 5 in question.

The main monitoring antenna 21 serves to synchronize the sequencing ofthe operation of the central unit 1 for the acquisition of the pressuretelemetry. This is because the radio circuits 13 here include only asingle radio-telemetry acquisition system, common to the four individualacquisition antennae 22 to 25, such that the microprocessor 11 has tocause a listening scan of the four transmitters from the wheels 2 to 5in order to acquire their transmissions.

These transmissions of trains of bursts occur with a burst period T of 1hour when the wheels 2 to 5 are stopped, or at least are turning only ata speed less than a lower threshold and, otherwise, every six minuteswhen the threshold is exceeded. Each transmission period includes fiveidentical bursts of information bits with an elementary period of 20milliseconds, each lasting 8 milliseconds and spaced by 12 milliseconds.

The polling by the microprocessor 11 is synchronized to thetransmissions from the wheels 2 to 5. To do that, the main antenna 21 isdesigned to detect the transmissions from all the wheels 2 to 5 and themicroprocessor 11 drives the changeover-switching circuits 13 so that,with the checking device in the rest state, it is the main monitoringantenna 21 which is linked to the common radio-reception system.

Thus, when the radio circuits 12 receive a first burst, themicroprocessor 11 is informed thereof and this reception causes apolling scan of the individual acquisition antennae 22 to 25, one ofwhich has also received the burst and will therefore receive thefollowing ones.

Having regard to the fact that there are five associated bursts on eachoccasion during one overall period of bursts, with known periodicityequal to 20 ms, it would have been possible to make provision to detectthe first burst then immediately to order successive polls of the fourantennae 22 to 25 for a period of 20 ms on each occasion, so as toreceive one of the next four bursts of the train and thus identify theindividual antenna 22 to 25 which is receiving the train of bursts.

Here, however, in order better to tolerate the faults in radiotransmission which are liable to make the received bursts unusable, themicroprocessor 11 waits until it has received three bursts of the trainfive bursts (FIG. 2B) before ordering the switching-over of thereceiving system from the main monitoring antenna 21 onto one of theindividual acquisition antennae 22 to 25, for example the antenna 22.Thus the microprocessor 11 drives the changeover-switching circuits 13so as to switch over from the main receiving antenna 21 onto one of theindividual receiving antennae 22 to 25 in the course of the same periodof bursts, over a little under one hundred milliseconds or so. FIG. 2Arepresents five trains of five bursts, as a function of time t. FIGS.2B, 2C, 2C, 2E and 2F represent polling windows for the respectiveantennae 21, 22, 23, 24, 25, that is to say the selection status of oneof the antennae as regards the radio-reception system controlled by thechangeover-switching circuits 13.

The switched-over state corresponding to the individual antenna 22 (FIG.2C) is maintained for at least two individual periods (40 ms) so as todetect the last two bursts of the train. If at least one of these lasttwo bursts represents a bit pattern, possibly after correction by aself-corrector code, similar to the bit pattern of at least one of thefirst three bursts received by the monitoring antenna 21, the wheel inquestion, 22, is identified as being the wheel transmitting the bursts.

In a variant, the microprocessor 11 may simply detect that themonitoring antenna 21 is receiving electromagnetic energy at a levelexceeding a defined threshold. The validation of the burst or burstsreceived by the acquisition antennae 22 to 25 is then independent of anyrecognition of a pattern in the bursts received by the monitoringantenna 21.

If the polled antenna (22) is not supplying a signal, or is supplying anunrecognized bit pattern, the microprocessor 11 orders thechangeover-switching circuits 13 to poll another acquisition antenna,such as 23, during a time window (FIG. 2D) centred on a future instant,as close as possible, of retransmission of the train of five bursts,that is to say about 6 minutes after the current instant. If the vehicleis unused, at rest, and if the wheels 2 to 5 are therefore transmittingonly every hour, the mapping of the positions of the wheelsindividualized in the central unit 1 is then slowed, but that does notpresent any drawback, because of the fact that the vehicle isimmobilized.

When the vehicle is running, the microprocessor 11 thus locates thetransmitting wheel 22 to 25 with a delay of 0 (FIG. 2C), 1 (FIG. 2D), 2(FIG. 2E) or 3 (FIG. 2F) periods T of 6 min.

The process is continued in order thus subsequently to locate two otherwheels 2 to 5 which are themselves transmitting and then to deduce theposition of the last wheel.

If the transmitter devices 20, 30, 40, 50 are transmitting, in thebursts, an identity codeword, specific to each of them, the central unit1 can draw up a table of the configuration of the wheels 2 to 5associating each identity codeword with an individual antenna 22 to 25,that is to say in fact to a wheel location 2 to 5. It is hence a matterof automatically determining the configuration of the checking system,that is to say the location of each of the wheel devices 20, 30, 40, 50.Once this configuration has been determined, the central unit 1 can useonly the main antenna 21 to monitor the four wheels 2 to 5, subject torenewing the configuration process when the vehicle is stopped for acertain length of time and when wheels 2 to 5 are then capable of beingchanged or exchanged.

In a variant, it is possible, in contrast, to carry on the polling ofthe individual antennae 22 to continuously, and it is then pointless totransmit the identity of the transmitter in each burst, which makes itpossible to shorten the bursts and thereby to save the batteries of thetransmitters.

What is claimed is:
 1. System for checking the pressure of the tires ofthe wheels (2-5) of a vehicle including individual wheel-checkingdevices, each with a pressure sensor and a transmitter (20, 30, 40, 50),a central unit (1) with a common receiver (12) and antenna circuits(21-25), comprising individual receiving antennae (22-25) associatedrespectively with the wheel locations (2-5), configured to work with thetransmitters (20, 30, 40, 50) of the individual checking devices, thesystem being characterized in that the receiving-antenna means of thecentral unit (1) additionally comprise a main antenna (21) formonitoring all the pressure-checking devices (20, 30, 40, 50) and means(13) for switching over the common receiver (12) of the central unit (1)from the main monitoring antenna (21) onto each of the individualacquisition antennae (22-25).
 2. System according to claim 1, in whichthe individual receiving antennae (22-25) are electromagneticallyassociated, in a one-to-one way, with the respective wheel locations(2-5).
 3. System according to claim 1 in which, with the wheel-checkingdevices (20, 30, 40, 50) being configured to periodically transmitbursts of information bits, the changeover-switching means (13) areconfigured to switch over from the main receiving antenna (21) onto anindividual receiving antenna (22-25) in the course of the same burstperiod.
 4. System according to claim 1, in which the antennae (22-25)are radiating cables.